1. Field of the Invention
The present invention relates generally to reinforcing large scale support structures which are present in high moisture environments. More particularly, the present invention involves reinforcing structures which are at least partially immersed in either fresh or salt water. Reinforcement is accomplished utilizing composite materials which are wrapped around the structures in situ to form underwater reinforcements. The invention is intended for use in those environments where toxicity to fish and other aquatic wildlife may be of concern.
2. Description of Related Art
Concrete columns are widely used as support structures. Bridge supports, freeway overpass supports, building structural supports and parking structure supports are just a few of the many uses for concrete columns. Concrete columns exist in a wide variety of shapes. Concrete columns with circular, square and rectangular cross-sections are most common. However, numerous other cross-sectional shapes have been used including regular polygonal shapes and irregular cross-sections. The size of concrete columns also varies greatly depending upon the intended use. Concrete columns with diameters on the order of 2 to 20 feet and lengths of well over 50 feet are commonly used as bridge or overpass supports.
It is common practice to reinforce concrete columns with metal rods or bars. The metal reinforcement provides a great deal of added structural strength to the concrete column. Although metal reinforcement of concrete columns provides adequate structural reinforcement under most circumstances, there have been numerous incidents of structural failure of metal-reinforced concrete columns when subjected to asymmetric loads generated during earthquakes. The structural failure of a metal reinforced concrete support column during an earthquake can have disastrous consequences. Accordingly, there is a continuing need to enhance the ability of concrete columns to withstand the asymmetric loads which are applied to the column during an earthquake.
One way of increasing the structural integrity of concrete columns is to include additional metal reinforcement prior to pouring the concrete column. Other design features may be incorporated into the concrete column fabrication in order to increase its resistance to asymmetric loading. However, there are hundreds of thousands of existing concrete supports located in earthquake prone areas which do not have adequate metal reinforcement or structural design to withstand high degrees of asymmetric loading. Accordingly, there has been a concentrated effort to develop systems for reinforcing such existing concrete columns to prevent or reduce the likelihood of failure during an earthquake.
One example of a method for increasing the structural strength of existing concrete structures is set forth in U.S. Pat. No. 4,786,341. In this particular patent, the outer surface of the concrete column is reinforced by wrapping a fiber around the column in a variety of different patterns. A problem with this particular method is the amount of time required to wrap a concrete column with a single fiber is time consuming and expensive.
One approach to reinforcing the exterior of an existing concrete support column is set forth in U.S. Pat. No. 5,043,033. In this patent, the exterior of the concrete column is wrapped with a composite material to form a shell surrounding the concrete column. The space between the outer composite shell and the concrete column is then pressurized by injecting a hardenable liquid.
Another approach, as set forth in U.S. Pat. No. 5,218,810 involves wrapping large columns with composite reinforcement layers to form a reinforcing shell which is in direct contact with the column surface.
Although the above reinforcement procedures are well-suited for reinforcing structures in relatively dry environments, they are not suitable for use where water is present. For example, numerous bridge supports columns include substantial portions which are located under water. Such underwater columns are present in both fresh water and salt water environments. Accordingly, there is a present need to provide composite type reinforcement methods and systems which can be used under water. One such method is described in PCT International Publication No. WO 97/44188.
In addition to concrete columns, there are numerous other types of structures present in high moisture environments which require periodic reinforcing. Pier or pilings in both fresh water and salt water are made from many different types of materials, including metal, wood and concrete. These types of structures are subject to continual deterioration from the elements. A method and system which can be used simply and efficiently to rehabilitate these types of structures would be extremely advantageous. It also would be desirable to provide such reinforcing structures without creating a toxic hazard to fish and other wildlife.
In accordance with the present invention, a method is provided for reinforcing a wide variety of structures which are located underwater or in other high moisture environments. The invention is based on the discovery that composite materials may be used successfully to reinforce structures in high moisture environments provided that certain epoxy resin compositions are utilized in the resin matrix of the composite.
The invention involves applying to the surface of the structure at least one uncured reinforcement layer to form an uncured shell surrounding the surface. The uncured reinforcement layer includes a fabric portion and an uncured resin portion. As a feature of the present invention, the uncured resin portions contains 80-120 parts by weight epoxy resin and 30-70 parts by weight of a conversion agent. Optionally, 1-10 parts by weight of a thickening agent may be included in the uncured resin. This type of resin, when cured, was found to be especially well-suited for use in providing high strength reinforcement structures in high moisture environments. The uncured resin may also contain up to 10 parts by weight or more of a coloring agent. The coloring agent is useful when it is desirable to hide underlying surface irregularities, such as cracks, or to otherwise provide a desired surface color.
As another feature of the present invention, a containment layer is placed around the uncured reinforcement layer to enhance the curing process in underwater situations or other high moisture environments. The use of stretch wrap as a containment layer is especially useful for support columns and other structures located in river or ocean environments where turbulent water flow or wave action presents unique problems with respect to applying and curing the composite reinforcement.
As an additional feature of the present invention, it was discovered that the above-specified resins were not toxic to aquatic life during the application and curing in underwater conditions.
The above discussed and many other features and attendant advantages of the present invention will become better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings.